The Atbash cipher is one of the oldest known substitution ciphers, originally used for the Hebrew alphabet. It works by mirroring the alphabet — the first letter swaps with the last, the second with the second-to-last, and so on. This tool encrypts and decrypts Atbash text instantly and is popular for puzzles, escape rooms, CTF challenges and teaching the basics of cryptography.
How it works
Atbash maps each letter to its mirror position in the 26-letter alphabet: A↔Z, B↔Y, C↔X, … M↔N. Mathematically, a letter at position i (0-25) becomes position 25 − i. Because the mapping is symmetric, Atbash is its own inverse — running ciphertext back through the same operation returns the original message, so there is no separate decode mode. Letters keep their case, and digits, spaces and punctuation pass through untouched.
Example
Encrypt the word GERA:
- G (7th letter) → T
- E (5th letter) → V
- R (18th letter) → I
- A (1st letter) → Z
So GERA becomes TVIZ, and running TVIZ back through Atbash returns GERA.
| Plain | A | E | G | M | R | Z |
|---|---|---|---|---|---|---|
| Atbash | Z | V | T | N | I | A |
The conversion runs entirely in your browser and nothing is sent to a server.